Power supply system



April 1956 c. w. MILLER POWER SUPPLY SYSTEM Filed Jan. 14, 1952ISnventor CZaf/es Zfl @Y/e'f United States Patent" POWER SUPPLY SYSTEMCharles W. Miller, Anderson, Ind., assignor to General MotorsCorporation, Detroit, Mich., a corporation of Delaware ApplicationJanuary 14, 1952, Serial No. 266,383

4 Claims. (Cl. 250-214) My invention relates to electrical powersupplies, and, more particularly, to a regulated power supply system forelectronic circuits that require a comparatively high operating voltagesuch, for example, as certain forms of automatic head lamp dimmingcircuits for motor vehicles.

For the purpose of securing the high sensitivity required forsatisfactory operation of automatic head lamp dimmer circuits, thephoto-multiplier type of photo-emissive photocell has been suggested foruse as the light sensitive pick-up device therein. Such photocellsrequire a high anode supply voltage of the order of 1,000 volts or more,and further require that the operating voltage supplied thereto beclosely regulated in order to prevent undesirable fluctuations in theoutput of the photocell. The supply voltage for most forms of automaticdimmer circuits heretofore proposed is cutomarily obtained from 'avibrator-type power pack which is energized from the vehicle battery,the output of which undergoes considerable variation with changes inengine speed and other electrical loads supplied thereby. Thus, althoughit is possible to obtain a high voltage output by employing a highvoltage secondary winding on the output transformer associated with avibrator-type power pack, this has been found unsatisfactory due to theexpense and difficulty of providing adequate voltage regulation at thedesired high voltage level.

In order to obtain a closely regulated high voltage supply from a highvibrator type power pack, it has been suggested to perform the voltageregulation at a lower voltage level at the output of the power pack and.to obtain the desired high output voltage by using a radio frequencyoscillator. A system of this type is disclosed in copending U. S. patentapplication S. N. 165,- 392, filed June 1, 1950, in the names of GeorgeW. Onksen and Charles W. Miller, and of common ownership with thisapplication.

, 2,740,902 Patented Apr. 3, 2

therefore, the operating etficiency thereof and which is stable inoperation.

For the purpose of accurately setting the voltage supplied to thephoto-multiplier tube, 1 have found it advantageous to be able to adjustthe output of the power supply system over a range of output values. Thepresent invention is an improvement over the system described in theabove-mentioned application wherein such means as have been provided foradjusting the output voltage depend upon changing the tuning of theoscillator which results in operating the oscillator at offdesignconditions instead of at its peak efiiciency and also tends towardunstable operation thereof.

Accordingly, it is the general object of my invention to provide animproved high voltage power supply system which furnishes a closelyregulated output voltage that may be varied over a wide range of outputvalues. Another object is to provide an improved oscillator suitable foruse in a high voltage power supply system. Still another object is toprovide an improved oscillator the output of which may be readilyadjusted over a wide range of output values without afiecting the tuningand,

- switch (not shown).

The preferred manner in which these and other objects are realized,together with the features and advantages attending my invention willappear more fully from the following detailed description andaccompanying draw ing which represents a schematic circuit diagram of anautomatic headlight dimmer system utilizing the embodiment of myinvention.

The schematic circuit diagram shown in the drawing comprises, ingeneral, a vibrator power pack 2 which supplies a rectified outputvoltage through a voltage regulator tube 4 to a high voltage highfrequency oscillator section 6 enclosed in dashed outline. The output ofthe high voltage section of the power supply is rectified and suppliedto a photo-multiplier tube 8 connected in the input of a dimming controlcircuit 10 which automatically controls the energizationof the high andlow beam filaments of a pair 'of' vehicle head lamps (not shown) inaccordance with the intensity of the illumination from 'an approachingvehicle impinging on the photocell.

The main source of power for operation of the above apparatus isobtained from the vehicle storage battery (not shown) which is connectedto an incoming power line 12 through a conventional headlamp energizingLine 12 is connected to a selector switch 13 and 14, and also suppliespower from the battery to' the vehicle head lamps (not shown) over aline 16 as explained hereinafter. The selector switch is manuallyoperated and determines from its position whether the vehicle head lightsystem shall be conditioned for standard foot switch operation or forautomatic operation. When the selector switch-is closed, power issupplied therethrough from the battery to the input of thevibrator'power pack 2 over line 22.

The vibrator power pack comprises a conventional synchronous typevibrator 24 and an output transformer 26 having primary and secondarywindings 28 and 30 connected to the terminals 32 and 34, respectively,of the vibrator as shown. As is well known in the art, such anarrangement is self-rectifying and serves to provide a high D. C. outputvoltage from a low D. C. input voltage. The input to the vibrator issupplied over line 22 which is connected to the midpoint or center tapof the transformer primary Winding 28 through a filter 36. The filter 36is formed by a radio frequency choke coil 38 connected in series withline 22 and a condenser 40 connected from one terminal of the choke coilto ground and serves to prevent high frequency disturbances occasionedby operation of the vibrator 16 from appearing on line 22 and affectingthe main power source. A resistor 42 and buffer condenser 43 areconnected in series 'across the outer terminals of the transformersecondary winding 30 and serve to prevent arcing of the vibratorcontacts and the appearance of high frequency transients in the outputof the power pack which is taken from the midpoint of the secondarywinding 30 through an output lead 44. The output of the power pack appears between lead 44 and ground and is filtered by a condenser 46connected therebetween.

The filtered output voltage of the power pack is supplied over lead 44to a resistor 48 which is connected to the voltage regulator tube 4which may be of the conventional cold cathode gas-filled variety. Theregulator tube comprises an anode 49 connected to the resistor 48 and acathode 50 connected to ground and functions to maintain the voltagebetween its anode and cathode substantially constant. The regulatedvoltage appearing across the electrodes of the regulator tube is furtherfiltered by conductor 52 to the high voltage high frequency section 6of'the power supply system.

The high voltage high frequency section 6 of the power supply system isconstituted, by an oscillator 56- which comprises a vacuum tube 58having aplate 59,; screen grid 60, control grid 61,-cathodev 62,.and-heater 63'; a tank circuit formed by a tuned parallel combination ofa primary inductance coil 66 anda variable: condenser 68 shunted by acondenser. 78;. a grid. circuit. formed by an inductance coil 72, which.is, inductively coupled to the coil 66 of .the tank circuitand aparallel, combination of av resistor 74 and condenser 76; and a. load:circuit which,

comprises a secondary coil, 78, inductively coupled to the primary coil66 and connected to, a high voltage'rectifier tube 88 having an anode81, cathode 82,...and heater 8-3.

The plate 59 of the tube: 58 is; connected to one. side.

of thetuned resonant tankxcircuit, tthe other side of the tank, circuitbeing connected through line 86. and. resistor 88, to ground. Screenelectrode. 60' is connected to an adjustable tap 90, on the resistor 88.The operatingvolt'age for the plate. 591 of the tube 58' is suppliedfromthevoltageregulator tube 4 through line 52 and inductance coil 66. Thisvoltage also appears across: the resistor 88 and a portion thereof isapplied. to. the screen electrode 60.

through the adjustable tap 90 for the purpose of varying,

thev conductivity of the tube.

The inductance coils 66, 67 and 78v are wound on a common core so as toform an air core transformer. Cell 66 may be thoughtof as the primaryand coil 78 the secondary of the transformer. nected to the. controlgrid 61 of the oscillator tube 58 with such polarity so as to aid thebuild up: of oscillations. Otherwise stated, the voltage induced in coil72 by current flowing in coil 66 is applied to thecontrol grid 61 inphase with the voltage induced in coil 66. The parallel combination ofthe resistor 74- and condenser 76- connected between one terminal of theinput coil 72 and ground is the conventional grid leak arrangementcommonly used in oscillator circuits. to limit the amplitude of thegenerated oscillations. Thecathode 620E the tube 58 is connected to thegrounded side of. the heater 63; the other side of which is connectedthrough a conductor 92 and conductor 22 to themain power source.

The primary or tank coil 66 of the oscillator is inductively coupled tothe secondary load coil 78 aud=produces a-highvoltage which is rectifiedby the high-voltagerectifier tube 88. The anode 81 of the rectifier tubeis. connected to one terminal of the coil 78'and"its-cathode 82connected to the grounded side of the heater 83, the ungrounded side ofwhich isconnected through line- 93 and conductor 92 to the main powersource. The rectified output of the high voltage high frequencysection-60f the power supply system appears between ground andcontuctor94 connected to one side of the secondary: load coil 78 and a filtercondenser 95 as-s h-own.

Conductor 94 is connected to a resistance terminal block 96, which isenclosed in dashed outline and com prises a plurality of resistors100-109, inclusive, connected in series between conductor 94 and ground,the number of resistances corresponding to the number of stages in thephoto-multiplier tube 8. The photo-mul tiplier tube is of conventionaldesign and comprises an anode 112, cathode 11 6, and'anumber ofdynodes128- 128, inclusive. Line 84, which is of negative polarity, isconnected through a protective resistor 130 to the cathode 116 of thephoto-multiplier tube 8. The intermediate points between the resistors100-189, inclusive, are-connected through similar protective resistors131-139, inclusive, to the dynodes 128-128 of the photo-multiplier tube.The protective resistors are providedto protect-the phototube fromdamage due to daylight illuininative impinging thereon.

The output electrode 112 of the photo rnultiplier tube 8 is connectedthrough line 142 to the input'of an automatic dimmer circuit which mayinclude anam- Inductance coil 72 isconsa ience plifier tube 144 having aplate 14-5, control grid 146, cathode 147' and heater 1'48. The cathode147 is connected to the ungrounded side of the heater which is energizedfrom the main power source through conductor 22. The control grid 146 isconnected to receive the output of the photo-multiplier tube and isfurther connected to a resistor 150 which isconnected in series with aresistor 151 and a potentiometer 152, the adjustable arm 153 of thelatter being connected to line 22.

Operating voltage for the plate of the amplifier tube 144 is suppliedthereto from the regulated output of the vibrator power pack 2, throughline 156 which is connected between the anode 49 of the voltageregulator tube 4 and a relay coil 158 in the plate circuit of the tube144. A condenser 160 is shunted across the relay coil 158.

Relay 158 comprises an armature 162 which is associated with a pair ofstationary contacts 163 and 16 4, the armature. being normally closedagainst contact 163. A resistor in series with a condenser 171 isshunted across armature 162 and. contact 164 of the relay to preventarcing the'rebetween. The armature 162' is connected through conductor173 and line 22 to the main power source. Stationary contact 163 isconnected through line 174 to the junction between resistors 150 and 151 in the grid circuit of the amplifier, while stationarycontact 164 isconnected through line 176 to the upper contact 179 of a manuallyoperable switch 178, 179'. and 186, which may be the standard beamchanging. foot switch customarily provided in motor vehicles.

Switch arm-.178 of the foot switch is connected in circuit with a relaycoil 182 having an armature 183 and a pair of stationary contacts 184and 185 which are associated with the high and low beam head lampfilament circuits through conductors 188 and 198, respectively. Armature183 is normally closed against stationary contact 184 when the relaycoil 182 is de-energized, in which condition the high beam filaments ofthe vehicle head lampsare energized through a circuit from the mainpower source, line. 16, armature 183, contact 184, and line 188 to thehigh beam filaments. With switch arm 1.78-of the foot switch depressedagainst lower contact 188, the relay coil182 is held energized and thelow beam filaments of the vehicle headlamps are thus energized. Forautomatic control over the vehicle head lamps, switch arm 178 of thefoot switch is closed on contact 179 thereof.

The operation of the automatic dimmer circuit is as follows. In theabsence of illumination incident on the photomultiplier tube, theamplifier tube 144 conducts sutficient current to energize relay 158 tomaintain its armature closed against contact 163 thereof, tie-energizingrelay 182, and the high beam filaments of the vehicle headlamps areenergized'from the main power source throughline 16, armature 183 andcontact 184 of relay 182, and line 188. 7

Upon encountering a distantly approaching vehicle, the output of thephoto-multiplier tube increases negatively so as to afiect'theconductivity of amplifier tube 144 and decrease the currenttherethrough. When the approaching vehicle has approached reasonablyclose so that the illumination therefrom is. sufiicient to de-energizerelay 158; the-armature 162 thereof isreleased to engage contact 164- toenergize the relay coil 182 from line 22 through ar'mature-162 andcontact 164 of relay 158, line 176, contact 179 and switch arm 178 ofthe foot switch, and line 192. With relay 182 thus energized, the headlamps are switched from high to low beam position. Manual control overthehead lamp beam condition may be had under these conditions by virtueof the overriding action of the foot-switch.

In order to hold'the head lamps in dim position after the headlamps ofthe approaching vehicle have been dimmedin response thereto, the dimmercontrol circuit iscausedto operate at an increased threshold ofsensitivity so as to prevent the amplifier tube 144 from returning toits original conductivity in view of the decreased illumination nowreceived from the dimmed head lamps of the approaching vehicle. Thisfunction is accomplished by automatically inserting resistor 151 andpotentiometer 152 in the grid circuit of the amplifier tube, theseelements having been previously shorted out of the grid circuit whenrelay 158 was energized. The output of the photo-multiplier tube thenflows through the series combination of resistors 150, 151 andpotentiometer 152 and develops a negative grid bias voltage thereacrossthat is suificient to maintain the amplifier tube 144 in substantiallynon-conducting condition. Upon removal of the external illuminationincident on the photocell, the amplifier is returned to its originaldark actuated condition, and the head lamps are switched from dim backto high beam.

A manually operated auxiliary foot switch 196, 197, which is connectedfrom ground through a resistor 198, conductor 199, and relay coil 158 tothe regulated output of the vibrator power pack, is provided to enablethe operator to return his head lamps, which have been dimmed by thebright lights of an approaching vehicle, to brightened condition uponfailure of the operator of the latter vehicle to dim his bright lights.When the dimmer control circuit is in dim condition, relay 158 isde-energized while relay 182 is energized through a circuit rom the mainpower source, lines 22 and 173, armature 162 and contact 164 of relay158, line 176, contact 179 and switch arm 178 of the standard footswitch, line 192 to the relay coil 182 and to ground. The standard footswitch is maintained in this position when automatic control over thevehicle head lamps is to be effected. Under these conditions, the dimmedhead lamps of the vehicle cannot be automatically returned to brightenedcondition to flash the operator of the approaching vehicle. However, byclosing the auxiliary foot switch, the relay 158 may be energizedthrough a circuit from the regulated output of the power pack, lines 156and 199, resistance 198 to ground, thereby de-energizing relay 182 andreturning the headlamps to brightened condition.

In order to operate the dimmer circuit under twilight conditions at dawnor dusk, a manually operated switch 201, 202 is provided to short thepotentiometer 152 out of the grid circuit of the amplifier tube 144.This switch functions to change the ratio of the sensitivity level ofthe dimmer system between the hold and dim positions sufiiciently toprevent natural twilight illumination from holding the head lamps intheir automatically dimmed condition after the vehicles have passed. Bydecreasing the resistance in the grid circuit of the amplifier controltube the grid bias, which is furnished by the voltage drop developedacross the total grid circuit resistance, for a given output from thephoto-multiplier tube is reduced which decreases the sensitivity of thesystem. Otherwise stated, the system requires a greater amount ofillumination on the photo-multiplier tube to hold the head lamps indimmed condition. It will be noted that the sensitivity of the systemwhen the control system is in bright position is unaffected.

Referring now more particularly to the power supply system of myinvention, its operation is as follows. D. C. power is supplied from thevehicle battery to the input of the vibrator power pack 2. Due tochanges in engine speed and in other electrical loads supplied by thebattery, the voltage supplied thereby may vary from, say 5.5 to 7.0volts which represents a variation of the order of 25%. Since theself-rectified output voltage appearing between the center tap andground of the transformer secondary winding 30 of the power pack issubject to approximately the same percentage variation, the secondarywinding thereof is designed to deliver a normal output voltage of theorder of 300 volts instead of the full 1100 volts, for example, requiredto operate the photo-multiplier tube 8. This is done to provide for 6regulating the output of the power pack at a voltage level that isrelatively low in comparison to the high voltage for thephoto-multiplier tube in view of the dilficulty and expense of obtainingsatisfactory voltage regulation at high voltage levels.

In the present system, the voltage regulation is obtained by the gaseousvoltage regulator 4 which is connected through its resistor 48 to theoutput of the power pack. Variations in the output of the power pack areabsorbed in the voltage drop across resistor 48 and the voltageappearing across the electrodes of the regulator tube is stabilized atapproximately 150 volts within plus or minus 2 volts.

The stabilized voltage appearing across the voltage regulator tube isthen supplied to the high voltage high frequency section 6 of the powersupply system which functions to generate a highly stable radiofrequency output voltage which is rectified and supplied to thephoto-multiplier tube 8 at the desired high voltage level. Theoscillator section 56 of the high frequency section of the power supplysystem is of the tuned plate variety and is tuned to generate a radiofrequency in the neighborhood of 350 kc., for example, which isintermediate the 455 kc. and 260 kc. intermediate frequencies employedin broadcast superheterodyne receivers. If desired an audio frequencyoscillator could be employed, but for reasons of economy and efiiciencya radio frequency oscillator is preferred. Tuning of the tank circuit ofthe oscillator is accomplished by varying the adjustable condenser 68therein until the voltage between line 94 and ground is at a maximum.The oscillator is then operating at maximum output and peak efiiciency.

In order to accurately set the operating voltage supplied to theelectrodes of the photo-multiplier tube for the most efficient operationthereof, it is desired that the output of the high voltage section ofthe power supply be adjustable over a range of output values. This isaccomplished in my invention by adjusting the position of the variabletap on resistor 88 so as to change the voltage applied to the screengrid 60 of the tube 58, thereby changing the conductivity thereof. Sincethe tuning of the oscillator tank circuit is not afliected, theoscillator continues to operate at its peak efficiency and to deliver ahighly stable output voltage, the magnitude of which may be adjustedover a wide range of values in accordance with the voltage applied tothe screen grid circuit thereof.

Further stability of the oscillator is afforded by the action of thecondenser 78 which is connected across the variable condenser 68 in theoscillator tank circuit. Condenser 70 is a conventional temperaturecompensated condenser, the capacitance of which changes in a negativedirection and oppositely to the change in capacitance of condenser 68with temperature changes. Thus, the frequency of the oscillator tankcircuit remains unaffected, with the result that the oscillator operatesat its maximum efficiency and delivers a highly stable output therefromfor substantially all operating conditions.

Although my invention has been shown and described in connection with aparticular form of automatic dimmer circuit, it may be employed equallywell with different types of dimmer circuits and still other forms ofelectronic circuits that require a closely regulated high voltage powersupply. it is to be understood that the above described arrangement isbut illustrative of the application of the principles of the inventionand that other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope thereof.

I claim:

1. A high-voltage power supply system comprising, in combination, asource of low-voltage D. C., means connected to said source to changethe low voltage D. C. to a higher voltage D. C., a voltage regulatortube connected to said voltage changing means to regulate the saidhigher D. C. voltage therefrom, a resistance connected across.

said voltage-regulator tube, means'for generating.an A.- C.-

voltage several timcs'higher than said higher D C. voltago, saidgenerating means includinga vacuum tubeoscillatorhavin'g a-plate, acathodeand apair of grid electrodes, a resonant tank circuit connectedto said plate electrodeand a connection from the high potential side ofsaid resistance across said voltage regulator tube to supply a-regulatedD. C. operating voltage through said resonant tank circuit to the saidplate electrode of said oscillator tube,- an input circuit connected toone of said grid electrodes and regenerativelycoupled to said tankcircuit, an adjustabletap on said resistance connected to the other ofsaid grid electrodes, an output circuit inductively coupledto said tankcircuit and high-voltage rectifying means connected in said outputcircuit for converting-the A. C. output voltage therefrom to D. C.

2. A stabilized high-voltage regulated power supply system comprising,in combination, a low voltage battery source ofD. C., vibrator powersupply means connected to said battery forchangiug said low voltage D.C. to a higher D.'C., a voltage regulator tube connected to saidvibrator power supply means to regulate the said higher D. C. voltagetherefrom, a resistance connected across said-voltage regulator tube,means for generating an A. C. voltage several times higher than saidhigher D. C. voltage, said generating meansineluding a vacuum tubeoscillator having a plate, a cathode and a pair of grid electrodes, aresonant'tank circuit connected to said plate electrode and having anegative temperature coefficient condenser therein, a connection fromthe high potential side of said resistance acrosssaid voltage regulatortube to supply a regulated D. C. operating voltage to the said plateelectrode of said oscillator tube, an input circuit connected to one ofsaid grid electrodes and regeneratively coupled to said tank circuit, anadjustable tap on said resistance connected to the other of said gridelectrodes, an output circuit inductively coupled to' said tank circuitand high voltage rectifying means connected in said output circuit forconverting the A. C. output voltage'therefrom to D. C.

3. in combination with an automatic headlight dimmer system having aphotomultiplier light pick-up cell requiringa high level D. C. operatingvoltage and an amplifier tube controlled from said pick-up cell andrequiring a considerably lower level operating voltage therefor, a lowvoltage batter-y source of D. C., vibrator power supply means connectedto said battery changing said low voltage D. C. to a higher D. C.voltage approximately in the range of that required for said amplifiertube of said automatic headlight dimmer system, means including avoltage regulator tube connected to said vibrator power supply means toregulate the said higher D. C. voltage therefrom, a resistance connectedacross said'voltage regulator tube and a connection from thehighpotential side of said resistance to supply a'regulated D.C/operating voltage to said amplifier tube of said automatic headlightdimmer system, means generating an A. C. voltage in the range of thatrequired for said photomultiplier tube of said automatic headlight-.dimmer'system includinga vacuum,

tube oscillator-havingza plate, cathode and at least two gridelectrodes,- a tuned tank circuit connected to' said plate electrode anda connection from the high potential side. of'said resistance acrosssaid voltage regulator tube to supply a regulated D. C. operatingvoltage to said plate electrode of said oscillator tube, an inputcircuit connected to one of said grid electrodes and regenerativelycoupled to said tank circuit, an adjustable tap on said resistanceacrosssaid voltageregulator tube connected to the other of said gridelectrodes of said vacuum tube oscillator and supplying an adjustableportion of said regulated D. C. voltage thereto, an output circuitcoupled to said tank circuit and high voltage rectifying means in saidoutput circuit converting'the high A. C. output voltage therefrom to ahigh level D. C. voltage for operating said photomultiplier tube of saidautomatic headlight dimmer system.

4. In combination withan automatic headlamp dimmer system having. alight sensitive pick-up device requiring a high. level operatingvoltageandan amplifier tube con trolled from said pick-up device andrequiring a lower level operating voltage, a power supply systemincluding a battery, a vibrator connected tosaid battery and supplyingan output voltage approximately in the'range of 'said amplifier tubeoperating voltage, voltage regulating means connected to said vibratorand maintaining the output voltage supplied therefrom substantiallyconstant, a con-.

nection from said'voltage regulating means to said amplifier tube tosupply a regulated operating'voltage thereto,

a vacuum tube oscillator havinga plate, a cathode and a pair of gridelectrodes, a tuned tank circuit connected to said plate electrode and aconnection from said voltage regulating means to said'tank circuitsupplying a regulated operating voltageto'theplate' electrode of theoscillator tube through thesaid'tank circuit thereof, an oscillatorinput circuit connected to one of the said grid electrodes of saidoscillator tube and regeneratively coupled to said tank circuit thereof,a potentiometer connected across said voltage regulating means andhaving an adjustable arm connected to the other of said grid electrodesof said oscillator tube,'and an output circuit coupled to the said tankcircuit of said oscillator tube and connected to said light sensitivepick-updevice of said automatic headlamp dimmer system'for' supplyinga'regulated high level opcrating voltage thereto.

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